The present project is concerned with the physiological mechanisms underlying recovery from brain damage in young, mature or aged rats. In the first study, rats were given either one-or two-stage lesions of the frontal cortex at approximately four months of age. After a short recovery period, the animals were tested to determine whether the serial lesions spared performance that is usually impaired when the damage is inflected in a single operation. At six month intervals, the rats are examined on a battery of tests designed to determine whether there is an age related change in recovery following serial or simultaneous lesions. Changes in behavior are then correlated with concommitant changes in CNS anatomy and these results are then related to ongoing, baseline experiments on the role of Nerve Growth Factor in promoting recovery from brain damage. Our initial results can be taken to indicate that in young, but mature rats, NGF facilitates behavioral recovery on some tasks but not others. Microscopic and biochemical analyses have not yet revealed the specific mechanisms by which NGF acts to improve postoperative performance in brain damaged animals, but these findings will serve as the basis for the second year projects currently being planned and developed.